2003 4.0 XLT Rear End Roar

[phillip723]

The rear end on my XLT started making a "roaring" noise when accelerating. It only happens above 35 mph and when my foot's on the gas, as soon as I let off it stops. The previous owner installed a new $2500 transmission and sold it to me when he got tired of the truck because the engine started ticking (lifters). Could the noise be the new transmission, or the rear diff maybe? I was thinking wheel barings but it only happens when accelerating.

 

[phillip723]

Actually, I just remembered that my transfer case doesn't have a vibration dampener on it. It's probably supposed to, right? LOL guess I have to find one

 

[Chrisincolumbus]

The rear end on my XLT started making a "roaring" noise when accelerating. It only happens above 35 mph and when my foot's on the gas, as soon as I let off it stops. The previous owner installed a new $2500 transmission and sold it to me when he got tired of the truck because the engine started ticking (lifters). Could the noise be the new transmission, or the rear diff maybe? I was thinking wheel barings but it only happens when accelerating.

Did you ever figure out what was causing the noise? Mine does the same above about 30mph and stops when you let off the gas. I had the rear diff fluid changed, but it didn't make any difference.

 

[imp]

Did you ever figure out what was causing the noise? Mine does the same above about 30mph and stops when you let off the gas. I had the rear diff fluid changed, but it didn't make any difference.

Alignment of ring and pinion gears lost due most likely to bad bearing(s) either on pinion gear or ring gear, but much more likely ring gear, since bad pinion gears howl like hell whether on the gas or not. imp

 

[ACQB]

Our 2003 started to whine/howl a few weeks back as it closed in 110,000 miles, any speed over 40mph. Really howled at 65-75mph. LOUD!
Changed the rear diff fluid shortly after the sound started. 3 weeks from sound started to servicing? Diff lube came out like thin'ish black tar....NASTY. Replaced with factory/dealer recommended conventual weight gear lube. 99.9999% of the "sound" went away immediately. Get a very slight howling sound at 70-74mph. No sound above or below that 'sweet spot'. Because it is such a different sound, not even sure its the diff making that sound at that speed. Only thing the same is the sound is coming from from the rear. Did a check on the rear wheel bearings, no play/wiggle felt, but that doesn't always mean there isn't an issue at select speeds.
Going to swap out the rear diff conventional lube for synthetic after 2000 miles of driving, drive it for a while then service the transfer case, then after more miles service the transmission. Randomly recheck the wheel bearings when it up in the air for other servicing. Doing one at a time so I can "listen" for changes.

 

[imp]

@ACQB
4X4? I pinpointed my rear noise by running up on stands, all 4 wheels clear, in 4X4 HIGH. (in AUTO, uneven brake drag causes big problems). Used long screwdriver as stethoscope, wife holding 30mph in drive, noise loudest at left wheel hub. Suspected diff. trouble, but steth. proved otherwise. Here's the bad bearing:





If

If you do this, use only sufficiently strong supports, and be careful, especially if not experienced working about moving parts! imp

 

[TechGuru]

wife holding 30mph in drive,

Is your cruise control broken?

 

[imp]

Is your cruise control broken?

@TechGuru
A smiley might have helped me figger out if yer jokin'. If you aren't, no it's not broken, would you lie under a vehicle with wheels running with no way to suddenly stop it? imp

 

[TechGuru]

@TechGuru
A smiley might have helped me figger out if yer jokin'. If you aren't, no it's not broken, would you lie under a vehicle with wheels running with no way to suddenly stop it? imp

Maybe, as long as it would be going away from me and not towards me and use a steth with a 3 foot tube so I could keep my distance.

https://www.harborfreight.com/mechanics-stethoscope-63296.html

 

[imp]

Maybe, as long as it would be going away from me and not towards me and use a steth with a 3 foot tube so I could keep my distance.

I do this process with the wheels removed, and rotors held down with a couple of snugged lug nuts. It saved me tearing into the axle housing, as I was certain that was the noise source before "stething". Not a process for the inexperienced, I should have emphasized. imp

 

[ACQB]

After driving a few more days & a few 100 more miles, the "noise", even in the above mentioned "sweet spot" is greatly diminished. Thinking a 2nd diff servicing may come sooner than originally planned. In this age of magic additives, is there a good one that I should use? There are a lot of snake oils out there as well. It is a standard diff, not the limited slip (that has a required MotorCraft additive).